The disclosure relates to noise reduction in a gas turbine and, more particularly, to the use of an acoustically treated feed pipe in an inlet bleed heat manifold for a gas turbine.
The combustion system of a gas turbine generates hot gases to drive a turbine. The turbine, in turn, drives a compressor that provides compressed air for combustion in the combustion system. The turbine produces usable output power. In some gas turbine applications, there are instances of gas turbine plant operation where the gas turbine pressure ratio reaches the operating pressure ratio limit of the compressor, resulting in compressor surge. These instances may arise in applications where low energy fuels or any other fuels with large amounts of diluent injection are used and/or at cold ambient temperature conditions. The compressor pressure ratio is typically larger than the turbine pressure ratio in that the latter is subject to pressure loss in the turbine combustor.
One solution that has been used to provide compressor pressure ratio protection is the bleeding off of gas turbine compressor discharge air and re-circulating the bleed air back to the compressor inlet. This method of gas turbine operation, known as inlet bleed heat (IBH) control, raises the inlet temperature of the compressor inlet air by mixing the bleed portion of the hot compressor discharge air with the colder ambient air, thereby reducing the air density and the mass flow to the gas turbine.
When a gas turbine bleeds compressor air into the inlet duct, it creates noise that can exceed noise limits. In one IBH system, a number of supply feed pipes with a number of orifices along their length are positioned across the inlet duct to deliver the bleed flow. In this setting, the compressed airflow exiting the orifices creates a loud sonic jet. In order to attenuate the noise generated by the sonic jets issuing out of the IBH feed pipes, the supply feed pipes are located downstream but as close as possible to an inlet silencer within the inlet housing, and upstream as far as possible from the compressor inlet. This positioning is also oftentimes required to attain required thermal mixing of the bleed flow with the inlet airflow to meet system parameters at the compressor inlet. The particular IBH system requires positioning that limits the allowable configurations for the IBH system and the inlet housing.
In another IBH system, an array of supply feed pipes with certain feed pipes having orifices along their length is provided. Each orifice is provided with an acoustically treated nozzle that extends perpendicular to the feed pipe. Each acoustically treated nozzle includes a port coupled to a respective orifice on the supply feed pipe, a metal-mesh containing container in fluid communication with the port and an outlet from the container having various openings through which the bleed flow may pass radially outward in a subsonic state. The metal mesh acts to attenuate noise such that the IBH system can be positioned upstream of the inlet silencer. While these nozzles act to mitigate the noise, they are costly and complicated. For example, an IBH system may require a large number of supply feed pipes and include hundreds of nozzles along the array of supply feed pipes with each orifice requiring an acoustically treated nozzle. Consequently, installation and/or repair can be time consuming and costly. In addition, this particular IBH system also requires positioning that limits the allowable configurations for the IBH system and the inlet housing.